The Q&A Archives: Ants on Shrubs and Trees

Question: Ants are crawling up and down one of our mature trees as well as several newly planted young pine trees. What are they doing and how can I get rid of them without harming the plants?

Answer: The ants you see probably aren't doing any harm themselves, but if you look more closely, you may find an aphid infestation. Aphids are tiny oval insects, sometimes called "plant lice," that congregate on new growth. They suck plant juices, producing a waste product called honeydew. Ants are often found near aphid colonies, feeding on the sticky, sweet honeydew.

If you can control the primary problem -- usually aphids, sometimes whiteflies or scale -- you'll control the ants as well. Aphids can often be kept in check by dislodging them with occasional sprays from a hose. If there are no aphids present, then look closely to see if the ants are causing any damage. Most often they prey on other insects or feed on plant sap that is already leaking from wounds caused by other insects or by physical damage.

There is also an inedible herb called tansy which works well as an ant (and other insect) repellent -- try planting a few in the garden in containers. (Don't plant it directly in the garden -- it can become invasive). It is an attractive flower, and the flower heads are often used in dried arrangements. Don't eat it, however.

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